As the automotive industry continues to focus on reducing the weight of vehicles to meet customer expectations on fuel economy and CAFE requirements, interest in alternative materials including carbon fiber composite applications has increased. In body-in-white structures, joining methods have traditionally relied on resistance-spot welding (e.g., in steel structures).
In the case of aluminum intensive vehicles and other mixed metal joining applications, self-piercing rivet technology prevails. One advantage of self-piercing rivet technology is that it is a high production volume assembly process. Self-piercing rivet technology is compatible with adhesive and both methods can be used together. The challenge often faced with self-piercing rivet technology, however, is that the substrate material must be ductile enough to form a “button”, i.e., protrusion, which is the result of creating the joint and the necessary deformation to provide mechanical interlock. When composite parts do not have sufficient ductility to form a button on the obverse side, fibers may be exposed through cracks in this surface. Surface cracking and fiber displacement are undesirable, as they may reduce the durability of the joint and result in premature failure. With a self-piercing rivet, fibers in the area where the rivet is inserted may result in surface cracking or fiber displacement.
Composite materials, such as carbon fiber, glass fiber or natural fiber composites, can be limited in application due to challenges relating to joining parts together. Frequently, these composites have limited ductility and are not well adapted to large displacements and deformation required to join parts together with self-piercing rivets.
Adhesives are used extensively to join composite parts together. Adhesive joining is a lower volume production method when used in isolation and is susceptible to displacement (i.e., movement between the parts to be joined) until the glue is cured.
Other methods, such as blind rivets, may be used to fasten parts to a composite component but it is necessary to first drill or pre-form a hole through the parts to insert the blind rivet. Assembly operations for drilling holes, aligning the holes, inserting the blind rivet and affixing the rivet add to the cost of assembly and the cost of tooling. A joining solution is needed that meets high volume production requirements and enables joining in a low ductility material.
This disclosure is directed to overcoming the above problems and other problems associated with the use of composite parts in applications where other parts are joined to a composite part.